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Conformation of amylose in aqueous solution: Optical rotatory dispersion and circular dichroism of amylose–iodine complexes and dependence on chain length of retrogradation of amylose
Author(s) -
Pfannemüller B.,
Mayerhöfer H.,
Schulz R. C.
Publication year - 1971
Publication title -
biopolymers
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.556
H-Index - 125
eISSN - 1097-0282
pISSN - 0006-3525
DOI - 10.1002/bip.360100203
Subject(s) - amylose , chemistry , aqueous solution , optical rotatory dispersion , degree of polymerization , retrogradation (starch) , circular dichroism , crystallography , iodine , cotton effect , absorption (acoustics) , molecule , stereochemistry , polymer chemistry , polymerization , organic chemistry , polymer , starch , physics , acoustics
The dependence on chain length of two characteristic properties of amylose, i.e., retrogradation and complex formation with iodine, have been studied by using enzymatically synthesized, homodisperse amyloses. The association rates of amyloses in water containing 5% dimethyl sulfoxide have a sharp maximum at a degree of polymerization P̄ n of 80; shorter and longer molecules are much more soluble. The iodine complexes of amylose exhibit a strong Cotton effect in the range of the long‐wave absorption maximum (position depending on chain length) and two weaker Cotton effects at 480 and 350 nm. The long‐wave Cotton effect is most intense at about P̄ n 50 and decreases rapidly for shorter and longer chains. This behavior is unexpected and is not in accordance with the further increase of λ max and λ max . The experiments can best be interpreted by assuming well ordered, stiff chains in the low molecular weight range (P̄ n 50–80). For longer chains, the findings are discussed in the light of current concepts of amylose conformation in aqueous solution, namely the model of the broken helical chain (alternating stiff helical segments and unordered regions) and the model of a flexible coil without a significant helical content. However, according to the results given in this paper, a wormlike helical chain seems to be the most adequate model for amylose conformation in neutral solution.